1. Field of the Invention
The present invention relates to a balloon catheter for pulmonary vein isolation and, more particularly, to a balloon catheter for atrium ablation for the treatment of a local lesion through local radio-frequency heating under pressure to treat atrial fibrillation.
2. Description of the Related Art
A known radio-frequency ablation method of electrically isolating a pulmonary vein repeats cauterization ten and some odd times to cauterize spots around the pulmonary vein successively with a catheter provided with metallic electrodes having 4 mm chips for the electric cauterization of the spots around the pulmonary vein. Most operations by this radio-frequency ablation method result in failure because the radio-frequency ablation method requires skilled catheter operation and is technically very difficult to achieve.
A radio-frequency ablation method of electrically isolating a pulmonary vein by radio-frequency heating using an inflatable balloon catheter is disclosed in Japanese Patent No. 2574119 issued to the applicant of the present invention.
The metallic electrodes having rough surfaces of the known catheter are exposed to blood. When the temperature of the electrodes is increased beyond a critical point by radio-frequency heating, thrombi are formed on the surfaces of the metallic electrodes. Therefore, a complication of thromboembolism arises when cauterization is repeated many times. The cauterization of many points one at a time takes a long time, which entails the hazard of exposure to radiation by x-ray fluoroscopy.
The radio-frequency ablation method disclosed in Japanese Patent No. 2574119 uses a large balloon capable of entirely occupying a right atrium to cover the ostium of all the four pulmonary veins. Therefore, the heart must be stopped temporarily and extracorporeal circulation must be effected by an artificial heart-lung apparatus.
Accordingly, it is an object of the present invention to solve those problems in the prior art and to provide a balloon catheter capable of forming a transmural necrotic layer around the pulmonary vein ostium without excessively cauterizing the endocardium and without forming thrombi, of cauterizing portions of the four pulmonary veins around the ostium of the same one by one and of achieving pulmonary vein isolation without requiring extracorporeal circulation.
Most causes of atrial premature beat that triggers atrial fibrillation, i.e., a kind of arhythmia, reside in the pulmonary vein. It has been recently found that atrial fibrillation can be prevented by electrically isolating those causes. The applicant of the present invention has developed various balloon catheters for radio-frequency heating, such as those disclosed in Japanese Patent Nos. 2538375, 2510428 and 2574119. Those patented balloon catheters are capable of easily cauterizing the inner surface of the pulmonary vein. Experimental data obtained by the applicant of the present invention showed that there is the possibility that those balloon catheters cause the restenosis of the pulmonary vein, entailing pulmonary hypertension. Therefore, the inventors of the present invention thought of a balloon catheter for pulmonary vein isolation without restenosis of pulmonary vein by circumferential ablation of the junction between the pulmonary vein and a left atrium, and the left atrium around the pulmonary vein.
To achieve the foregoing object, according to one aspect of the present invention, a balloon catheter for pulmonary vein isolation comprises: a catheter shaft consisting of a tubular outer shaft and a tubular inner shaft; an inflatable balloon, which has a larger diameter than that of the pulmonary vein ostium capable of contact with a predetermined annular portion of pulmonary vein ostium when inflated and having one end portion connected to the extremity of the tubular outer shaft and the other end portion connected to the extremity of the tubular inner shaft; a radio-frequency electrode paired with a electric plate placed on the surface of the patient""s body to transmit radio-frequency power and placed in a wall forming the balloon or in the balloon; a lead wire connected to the radio-frequency electrode; a cooling means for pouring cooling liquid to cool the respective interior of the catheter shaft and the balloon; and a temperature sensor for measuring temperature in the balloon.
Preferably, the balloon as inflated has a shape resembling an onion having a larger diameter than that of pulmonary vein ostium on the side of the tubular outer shaft of the catheter shaft.
Preferably, the balloon as inflated has a shape resembling a mushroom having a larger diameter than that of pulmonary vein ostium on the side of the tubular outer shaft of the catheter shaft.
Preferably, the radio-frequency electrode is wound round the tubular inner shaft of the catheter shaft.
Preferably, the radio-frequency electrode is formed in a circular shape on the inner surface of the wall of the balloon so as to be located close to the predetermined portion when the balloon is inflated.
Preferably, the predetermined portion is the junction between the pulmonary vein and the left atrial wall.
Preferably, the predetermined portion is a portion of the left atrial wall around a pulmonary vein.
Preferably, the cooling means circulates cooling liquid.
Preferably, a U-shaped cooling liquid passage through which the cooling liquid can be circulated is formed in the tubular inner shaft of the catheter shaft.
Preferably, radio-frequency power is supplied to the radio-frequency electrode to heat the balloon at a predetermined temperature and the temperature of the balloon is monitored by means of the temperature sensor.
Preferably, radio-frequency power is supplied to the radio-frequency electrode so that impedance between the radio-frequency electrode and the electric plate is in a predetermined impedance range and the impedance between the radio-frequency electrode and the electric plate is monitored.
Preferably, the tubular outer shaft, the tubular inner shaft and the balloon are formed of an antithrombotic resin and have smooth surfaces, respectively.
Since the balloon is capable of coming into contact with the predetermined annular portion of a pulmonary vein ostium when inflated, the annular portion of the of each pulmonary vein ostium can be individually cauterized without requiring extracorporeal circulation. Since the respective interiors of the catheter shaft and the balloon can be cooled, the excessive heating of the catheter shaft by the lead wire and the radio-frequency electrode and the resultant deformation of the catheter shaft can be prevented. Since the temperature of the interior of the balloon is measured by the temperature sensor, a transmural necrotic layer can be formed without excessively cauterizing the endocardium.